1. Field of the invention
This invention relates to an improved storage stable formulations. The invention particularly relates to an improved storage stable formulations of mutually incompatible active ingredients such as a Chloronicotynyle compound and an Organophosphorus compound. The invention more particularly relates to an improved storage stable formulation of mutually incompatible active ingredients such as Acephate and Imidacloprid. The present invention also relates to a process for the preparation of the above said storage stable formulation. The storage stable formulation of the present invention is useful for the protection of crops.
2. Description of Related Art
Enhancement of the agricultural produce requires the protection of the crops and its produce from pest damage. Various chemicals and their formulations have been developed and are in use currently for the effective management of the insect pests. Due to non-judicious use of the hitherto known pesticides, the pests gain resistance and it becomes difficult to kill them. The need for more food has to be met through higher yields per unit of the land, water, energy and time. Excessive use of mineral, fertilizers and chemical pesticides has caused soil degradation, ground water pollution and the spread of the pests resistant to pesticides in several areas. It, therefore, becomes necessary to have formulations of at least one or more pesticides formulated in such a way that they show an additional and/or better activity thereby exhibiting synergy.
Processes for preparing pesticidal agents and compositions have been developed to control pests. However, processes, which are economically efficient and provide ecologically safe pest control compositions, are still being sought. It is highly desirable to have a process for the preparation of pesticidal compositions, which allow for reduced effective dosage rates, increased environmental safety and lower incidence of pest resistance. Further, even though combinations of pest control agents have been studied, a high synergistic action has not always been found. Often, these mixtures show very low activity instead of the expected activity level either due to the intrinsic incompatibility of the active ingredients used and/or due to the product instability caused as a result of the incompatibility, thereby giving a shorter shelf life. In such cases, formulating these actives so as to achieve the best results of the combination poses a major hurdle.
A tank-mix of the two actives may or may not demonstrate synergy even if it is used in a certain manner by knowledgeable and skilled people under certain specific conditions. It is not pre-formulated and, therefore, can also prove to be a hazard during transport.
The above limitation may be overcome by providing a ready-to-use pre-formulated product. A pre-formulated product has many advantages including reduced handling, reduced risk of dosage error, reduced packaging, etc. However, this becomes difficult if the active ingredients used are unstable when mixed together.
This can be overcome by coating one of the actives by a barrier or a protective coat, which is the focus of the present invention.
One such example is that of Acephate and Imidacloprid, which are unstable when formulated together. Acephate is a systemic insecticide belonging to the phosphoroamidothioate class of compounds. It is used for control of a wide range of biting and sucking insects, especially aphids, including resistant species, in fruit, vegetables (e.g. potatoes and sugar beets), vine, and crop cultivation and in horticulture (e.g. on roses and chrysanthemums grown outdoors). It also controls leaf miners, lepidopterous larvae, sawflies and thrips in the previously stated crops as well as turf, mint and forestry. Acephate is unstable in alkaline pH and starts degrading.
Imidacloprid is a systemic, chloro-nicotinyl insecticide with soil, seed and foliar uses for the control of sucking insects including rice hoppers, aphids, thrips, whiteflies, termites, turf insects, soil insects and some beetles. It is most commonly used on rice, cereal, maize, potatoes, vegetables, sugar beets, fruit, cotton, hops and turf, and is especially systemic when used as a seed or soil treatment. The chemical works by interfering with the transmission of stimuli in the insect nervous system. Specifically, it causes a blockage in a type of neuronal pathway (nicotinergic) that is more abundant in insects than in warm-blooded animals (making the chemical selectively more toxic to insects than warm-blooded animals). This blockage leads to the accumulation of acetylcholine, an important neurotransmitter, resulting in the insect's paralysis, and eventually death. It is effective on and via stomach action. Imidacloprid is stable to hydrolysis at pH 5-11.
While Acephate is unstable in alkaline pH, Imidacloprid is unstable in acidic pH and it is difficult to formulate them together.
In the case of Acephate, since the rate of hydrolysis increases with increasing pH, degradation occurs more rapidly in alkaline soil than in acidic soil. Hence, it is necessary to protect the active from degradation to form its metabolites, which may or may not show any pesticidal activity and may be toxic. Therefore, it becomes necessary to formulate such incompatible actives in such a way as to enhance their synergistic property, making them storage stable compositions
A process for preparing a coated pesticidal matrix, which protects the pesticidal activity of the active ingredient by coating it with a pH-dependent polymer already exists in the prior art.
A process also exists for making ingestible insecticide compositions comprising entrapping the insecticide in a suitably charged polymer in aqueous medium, then modifying the charge of the polymer to cause precipitation of the polymer thereby entrapping the insecticide in it.
However, synthetic or non-biodegradable polymers pose a problem to the environment and are therefore, not preferred. Naturally occurring polymers are better suited for this purpose and have been used in various controlled release formulations.
Pesticide granules, which were prepared by blending the pesticide with solid carriers and extruded are also known. The extruded granules were then coated with a solution of binder and optionally with a solution of a dispersant and finally dried.
Inorganic polymer complexes for controlled release of compounds comprising a hydrated or crystallized inorganic compound and a matrix polymer which slows down the release of the active agent also are known.
The production and use of inorganic-conditioning agent complexes comprising of resorbable matrices formed by mixing an inorganic compound capable of undergoing hydration and/or crystallization, a conditioning agent that improves stability, a matrix polymer and/or a complexing agent are also known. The system can be used for controlled release of actives.
Water dispersible, dry, flowable granules of agricultural chemicals, such as quinclorac, which are coated with a water-soluble coating layer of polyvinyl alcohol are known. The granules are formulated to reduce or eliminate any chemical residue on interior surfaces of containers used to package the formulations for transport/handling thereby enhancing the safety. The drawback of using polyvinyl alcohol is that it has a high melting point and hence the reaction will involve high temperatures at which active ingredients like Acephate will degrade. So, this polymer is unsuitable for active ingredients that are heat-unstable. Besides this, the process of coating is carried out by dissolving polyvinyl alcohol in water. This makes it unsuitable for using with active ingredients that are moisture-sensitive. Acephate is also sensitive to moisture and degrades rapidly, so this method is not advisable for compositions containing Acephate.
Other polymers, which are not water-soluble, have limitations and in compositions where one of the active ingredients is soluble in the organic solvent used for dissolving the polymer, the release of such active would pose a problem.